Jökull - 01.10.1998, Page 54

DISCUSSION AND SUMMARY
The four years considered in this study show spa-
tial distribution and temporal variations which reflect
climatological conditions; large variations are ob-
served in the accumulation, ablation and runoff of
Vatnajökull. These years, however, do not illustrate
the full scale of climatic variability and extremes that
can be expected (Figs. 13-15). The specific winter
balance may have been above average, albeit fairly
constant over the period 1991 to 1995 but the sum-
mers were cold compared with an average after 1940.
There is, however, a trend of warmer summers after
1985 but only one of the four summers (1994) was
Fig. 13. Long-term records of winter precipitation (Septem-
ber-May) and summer temperature (May-September) at
three weather stations in Iceland (See Fig. 1). Veðráttan
(1924- 1995).
- Vetrarúrkoma (sept.-maí) og sumarhiti (maí-sept.) á
þremur veðurstöðvum á Islandi.
warmer than the average over that period (Fig. 15).
The annual net balance, decreased year by year but
only one of the years showed negative mass balance
(Figs. 16 and 17). Further observations should be con-
ducted to describe the temporal climatic variability
that leads to negative mass balance of Vatnajökull.
The average net mass balance was positive in 1991-
1992 and 1992-1993 on all the outlets, only on the
northern outlets in 1993-1994, when the mass balance
of the westem outlets was slightly negative, and in
1994-95, only Dyngjujökull had a slightly positive
mass balance. During the cold summer of 1993, the
summer balance removed only 20-30% of the winter
balance on the northern outlets but snowfall during
the summer did not reach to western Vatnajökull
(Tungnaárjökull) which was fairly sunny with consid-
erable melting. The summer 1994 was the warmest of
the four summers, but the summer of 1995 was out-
1980 1985 1990 1995 2000
Year
Fig. 14. Winter precipitation (September-May) and summer
temperature (May-September) at four wheather stations
close to Vatnajökull from 1980 to 1995. Veðráttan (1980-
1995).
- Vetrarúrkoma (sept.-maí) og sumarhiti (maí-sept.) á
fjórum veðurstöðvum á Islandifrá 1980 til 1995.
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JOKULL, No. 45, 1998